The invention relates to a new supported catalyst and a process for its preparation, and its use for the preparation of hydroxydiphenyl.
A process for the preparation of o-phenylphenol(2-hydroxydiphenyl) by dehydrogenation of cyclohexanone derivatives in the presence of a supported catalyst is known from DE-OS No. (German Published Specification) 2,211,721. The catalyst employed in this process is prepared by depositing a very small amount of palladium, platinum, iridium or rhodium or a mixture of two or more of these elements onto a support, such as silica, aluminium oxide, silica/aluminium oxide or active charcoal, and furthermore adding a suitable amount of an alkali metal. In the Offenlegungsschrift (Published Specification) mentioned, it is found in particular that platinum and palladium have an especially high activity for selective formation of the desired product. The noble metal catalysts employed in this process, however, have too low a selectivity (especially when a rhodium-containing catalyst is used), an inadequate activity or too short a life (in this connection, compare the comparison example).
It is furthermore known from German Patent Specification No. 2,049,809 that hydroxydiphenyl can be prepared by catalytic dehydrogenation of compounds and/or compound mixtures consisting of completely and/or partly hydrogenated hydroxydiphenyl, in the presence of a dehydrogenation catalyst containing nickel, chromium, aluminium, copper and alkali metal. U.S. Pat. No. 4,060,559 likewise describes a process for the preparation of o-phenylphenol by dehydrogenation of cyclohexylphenol, which is carried out in the presence of a supported catalyst containing platinum or palladium. Disadvantages of these processes are likewise the relatively short life of the catalyst and the partly inadequate activity.